We are engaged in studies of cytokines that regulate cells of the myeloid lineage, and have focused primarily on the ability of IFN-gamma, IL 2 and picolinic acid to regulate macrophage (Mphi) tumoricidal activity. The mouse Mphi cell line ANA-1 Mphi does not express constitutive cytotoxic activity against P815 mastocytoma cells. However, these Mphi become activated after coincubation with IFN-gamma plus IL 2, or IFN-gamma plus picolinic acid. IL 4 inhibits IFN-gamma plus IL 2-induced and IFN-gamma plus picolinic acid-induced tumoricidal activity but not IFN-gamma plus LPS-induced tumoricidal activity. Both IL 2 and picolinic acid augment IFN-gamma-induced reactive nitrogen intermediate (RNI) production; and the ability of IL 2 and picolinic acid to induce Mm tumoricidal activity correlates directly with the metabolism of L-arginine to RNI. TNF-alpha is a required intermediate for IL 2-dependent, but not picolinic acid-dependent, tumoricidal activity in ANA-1 Mphi. Although IL 2 by itself does not induce tumoricidal activity in Mphi, IL 2 alone induces the production of a factor(s) from Mphi which is chemotactic for normal peritoneal Mphi. IL 2 also induces the expression of JE/MCP-1 mRNA in ANA-1 Mphi. Studies revealed that JE/MCP-1 may be at least one of the chemotactic factors induced in Mphi after exposure to IL 2 alone. We are pursuing a molecular cloning project designed to identify and characterize novel genes in cytotoxic mouse Mphi. Several clones have been isolated from two independent cDNA libraries that were prepared using mRNA isolated from either IFN-gamma- or IFN-gamma plus IL 2- treated Mphi. One of the cDNA clones is constitutively expressed in Mphi, and its expression is augmented after treatment of the Mphi with IFN-gamma. The cDNA has been sequenced and represents a novel gene on the basis of computer database searching. An interesting feature of the cDNA clone is the presence of a relatively unique repeated nucleic acid sequence that is found in mouse IL 2 cDNA and several other functionally unrelated eukaryotic genes.